Implantable medical devices are often equipped to deliver more than one type of therapy. For example, an implantable pulse generator (IPG) can deliver multiple types of therapy to the heart. A pacing therapy may be appropriate to address bradycardia or slow a stable but rapid heart rhythm. A pacing therapy typically comprises one or more low energy pulses that capture cardiac tissue and set off a depolarization wave. Another type of cardiac therapy is defibrillation therapy. Defibrillation therapy typically comprises a high energy shock that interrupts a rapid and unstable arrhythmia (e.g., fibrillation) in an attempt to reset the heart to a normal cardiac rhythm. The energy level of a pacing pulse is considerably lower than the high energy shock of defibrillation therapy, and as such a pacing therapy can be classified as a low voltage (LV) therapy and defibrillation therapy can be classified as a high voltage (HV) therapy. For example, the energy of a pacing pulse is typically between approximately 5 and 100 microjoules while the energy of a defibrillation shock is typically between approximately 5 and 40 joules. Different leads, which are used to convey therapeutic electrical energy from the IPG to the heart, can be configured in different ways to deliver respective LV and HV therapies. For example, one type of quadripolar lead may have four LV electrodes (LLLL) while another type of quadripolar lead may have two LV electrodes and two HV electrodes (LLHH).
An IPG typically includes bores (e.g., in a header) into which leads can be inserted to mechanically and electrically connect the leads to the IPG. The bores may be dimensioned similarly (e.g., per ISO 27186:2010), such that different types of leads can be placed in different bores of an IPG, even though each bore may be intended to be used with only a particular type of lead (e.g., by having particular channels routed to the bore). In some cases, the bores and leads may not be dimensioned to allow complete insertion of one type of lead (e.g., a LV lead) into a particular bore (e.g., a HV bore). Even so, electrical contact may occur on some or all of the electrodes of a lead if inserted into the wrong bore. A lead may be unintentionally inserted into a bore that is dimensioned to at least partially accept the lead but the type of therapy that the IPG is configured to deliver through the bore and the type of therapy that the lead is configured to deliver may not match, which is an example of lead reversal.
Hazards may exist with lead reversal. For example, it may be unlikely that a defibrillation shock therapy can be effectively delivered using a LV lead that only has electrodes designed for the delivery of LV therapy. Also, delivering defibrillation shock therapy using a LV lead could risk burning the tissue surrounding the LV lead's small electrodes because the small electrodes are not designed to transfer such a large amount of energy to tissue. Finally, the implanted system might be permanently damaged by delivering defibrillation shock therapy through a LV lead or by another unintended arrangement.